Control valve for variable displacement compressor

ABSTRACT

To provide a control valve for a variable displacement compressor, based on a Pd−Ps differential pressure control method, which is capable of setting characteristics concerning the degree of influence of crank pressure on a change in the differential pressure between discharge pressure and suction pressure, to desired characteristics with ease. A control valve for a variable displacement compressor adjusts the difference between an effective pressure-receiving area A on a discharge pressure side of an intermediate in which a valve element and a shaft are integral with each other and an effective pressure-receiving area B on a suction pressure side of the intermediate, as required. This makes it possible to obtain desired differential pressure·crank pressure characteristics according to the specifications of the control valve. Changes in the effective pressure-receiving areas have almost no influence on electric current·differential pressure characteristics, i.e. the relationship between the value of electric current supplied to a solenoid and the differential pressure between discharge pressure and suction pressure, and hence it is possible to realize the changes in the effective pressure-receiving areas with ease.

CROSS-REFERENCES TO RELATED APPLICATIONS, IF ANY:

This application claims priority of Japanese Application No. 2004-239161 filed on Aug. 19, 2004 and entitled “CONTROL VALVE FOR VARIABLE DISPLACEMENT COMPRESSOR”.

BACKGROUND OF THE INVENTION

(1) Field of the Invention

The present invention relates to a control valve for a variable displacement compressor, and more particularly to a control valve for a variable displacement compressor, for controlling a discharge capacity of refrigerant discharged from a variable displacement compressor for an automotive air conditioner.

(2) Description of the Related Art

A compressor used in a refrigeration cycle of an automotive air conditioner is driven by an engine whose rotational speed varies depending on a traveling condition of the vehicle, and hence incapable of performing rotational speed control. To eliminate the inconvenience, a variable displacement compressor capable of changing the discharge capacity of refrigerant is generally employed so as to obtain an adequate refrigerating capacity without being constrained by the rotational speed of the engine.

In a typical variable displacement compressor, a swash plate is disposed within a crankcase formed gastight, such that the inclination angle thereof can be changed, and driven by the rotational motion of a rotational shaft, for performing wobbling motion, and pistons caused to perform reciprocating motion in a direction parallel to the rotational shaft by the wobbling motion of the swash plate draw refrigerant from a suction chamber into associated cylinders, compress the refrigerant, and then discharge the compressed refrigerant into a discharge chamber. In doing this, the inclination angle of the swash plate can be varied by changing the pressure in the crankcase, whereby the stroke of the pistons is changed for changing the discharge capacity of the refrigerant. The control valve for a variable displacement compressor provides control to change the pressure in the crankcase.

In general, the control valve for variably controlling the discharge capacity of the compressor decompresses part of refrigerant discharged at discharge pressure Pd from the discharge chamber to introduce the decompressed refrigerant into the crankcase, and controls pressure Pc in the crankcase (crank pressure) through control of the amount of the refrigerant thus introduced. The control of the amount of the introduced refrigerant is realized by supplying external electric current to a solenoid provided in the control valve for control of actuation of a valve element in the control valve, specifically, by a method based on suction pressure Ps in the suction chamber, for example. In this method, the control valve senses the suction pressure Ps, and controls the flow rate of refrigerant introduced at discharge pressure Pd from the discharge chamber into the crankcase such that the suction pressure Ps is maintained at a predetermined level. The value of suction pressure Ps at which the variable displacement operation is to be started can be freely set according to the amount of electric current supplied to the solenoid.

However, to perform the displacement control based on the suction pressure Ps as described above, it is necessary to movably arrange a flexible member, such as a diaphragm or a bellows, for sensing the suction pressure Ps in the control valve, which tends to make the control valve relatively large in scale.

To eliminate the inconvenience, another method is sometimes employed which performs the control based on the differential pressure (Pd−Ps) between the discharge pressure Pd and the suction pressure Ps (hereinafter this control is referred to as “the Pd−Ps differential pressure control”). In the Pd−Ps differential pressure control, the differential pressure (Pd−Ps) between the discharge pressure Pd and the suction pressure Ps is sensed and the flow rate of refrigerant introduced at the discharge pressure Pd from the discharge chamber into the crankcase is controlled such that the differential pressure (Pd−Ps) is maintained at a predetermined level. The control valve for the control method is configured such that an effective pressure-receiving area of an intermediate, which comprises e.g. a valve element and a piston rod, for receiving the discharge pressure Pd, and an effective pressure-receiving area of the intermediate for receiving the suction pressure Ps, are made equal to each other such that the crank pressure Pc applied to the intermediate is cancelled. With this configuration, a valve section of the control valve performs an opening/closing operation by the differential pressure (Pd−Ps) between the discharge pressure Pd and the suction pressure Ps, irrespective of the crank pressure Pc (see e.g. Japanese Unexamined Patent Publication (Kokai) No. 2003-328936 (Paragraph numbers [0040] to [0045], FIG. 3)).

According to the control valve for the control method described as above, the discharge pressure Pd and the suction pressure Ps are directly received by the valve element for sensing the differential pressure therebetween, and hence it is possible to dispense with the above-mentioned flexible member. Particularly, since the discharge pressure Pd is directly sensed, it is possible to reflect a change in pressure of the variable displacement compressor as it is, and hence realize displacement control with excellent response.

As described above, originally, the Pd−Ps differential pressure control should be performed according to the value of electric current supplied to the solenoid, irrespective of the crank pressure Pc, such that the differential pressure (Pd−Ps) between the discharge pressure Pd and the suction pressure Ps is maintained at a predetermined level. However, actually, the crank pressure Pc is increased by increasing the differential pressure (Pd−Ps), and conversely the differential pressure (Pd−Ps) as well is varied to some extent in a manner affected by a variation in the crank pressure Pc, etc. More specifically, as the crank pressure Pc increases, the differential pressure (Pd−Ps) increases with a slight slope, for example.

Although the phenomenon may not be ideal when considering only the characteristics of the control valve, this is not always true when considering matching between the Pd−Ps differential pressure control and control of the variable displacement compressor. More specifically, when the differential pressure (Pd−Ps) instantaneously rises to a fixed value in response to a change in the value of electric current supplied to the solenoid, the valve section is instantaneously opened, which enhances the response of the swash plate of the variable displacement compressor, but nevertheless hunting or overshooting is sometimes caused in the displacement control. This makes it difficult to perform the displacement control with stability. On the other hand, when the differential pressure (Pd−Ps) is slow in rising, the response of the swash plate is degraded. Further, even with the same current value, the value of the differential pressure (Pd−Ps) to be controlled varies with the value of the crank pressure Pc. This sometimes leads to hysteresis of the displacement control, and hence is not preferable for control of the variable displacement compressor. Therefore, it is considered preferable to cause the differential pressure (Pd−Ps) to rise with a proper response (slope) according the value of electric current. For example, when the swash plate of the variable displacement compressor is difficult to move, it is required to increase the response to improve motion of the swash plate, whereas when the swash plate is excessively easy-to move, it is required to lower the response to stabilize motion of the swash plate.

To this end, the degree (slope) of influence of the crank pressure Pc on a change in the differential pressure (Pd−Ps) has conventionally been adjusted e.g. by changing the characteristic of a spring for urging the valve element in the moving direction thereof or changing the attractive force characteristic of the solenoid according to characteristics required of the control valve. However, when the characteristic of the spring or the attractive force characteristic of the solenoid is changed as described above, the differential pressure characteristics, i.e. the relationship between the value of electric current supplied to the solenoid and the differential pressure (Pd−Ps) can also be changed, which makes it difficult to perform a total tuning operation.

SUMMARY OF THE INVENTION

The present invention has been made in view of these problems, and an object thereof is to provide a control valve for a variable displacement compressor, based on a Pd−Ps differential pressure control method, which is capable of setting characteristics concerning the degree of influence of crank pressure on a change in the differential pressure between discharge pressure and suction pressure, to desired characteristics with ease.

To solve the above problem, the present invention provides a control valve for a variable displacement compressor, the control valve being mounted in the variable displacement compressor, for controlling pressure in a crankcase of the compressor to thereby vary a discharge capacity of refrigerant, comprising a body that has a discharge pressure port for introducing discharge pressure of the compressor, a crank pressure port for delivering crank pressure generated in the control valve to the crankcase, and a suction pressure port for introducing suction pressure, the discharge pressure port, the crank pressure port, and the suction pressure port being sequentially arranged from one end of the body, a valve element that is moved to and away from a valve seat provided between the discharge pressure port and the crank pressure port, for reducing the discharge pressure introduced from the discharge pressure port by a restriction passage formed between the valve element and the valve seat to generate the crank pressure, a shaft that supports the valve element in a valve-opening or valve-closing direction and is capable of operating in unison with the valve element, and a solenoid that is connected to an end of the body, opposite to the discharge pressure port, and comprises a core, a plunger capable of being made integral with the valve element via the shaft, and a solenoid coil for being energized to generate a magnetic circuit including the plunger and the core, wherein a degree of influence of the crank pressure on a change in differential pressure between the discharge pressure and the suction pressure is adjusted by adjusting a difference between an effective pressure-receiving area of an intermediate for receiving the discharge pressure, the intermediate being formed by making the valve element and the shaft integral with each other, and an effective pressure-receiving area of the intermediate for receiving the suction pressure.

It should be noted that there is described a feature “a plunger capable of being made integral with the valve element via the shaft”, the plunger need not necessarily be directly connected to the shaft, but it may be connected to the shaft via an interposed object formed separately from the shaft.

The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the arrangement of a control valve for a variable displacement compressor, according to an embodiment of the present invention.

FIG. 2 is a fragmentary expanded cross-sectional view of an upper portion of the FIG. 1 control valve.

FIG. 3A to 3C are diagrams useful in explaining differential pressure·crank pressure characteristics of the control valve for a variable displacement compressor.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a cross-sectional view showing the arrangement of a control valve for a variable displacement compressor, according to the present embodiment, and FIG. 2 is a fragmentary expanded cross-sectional view of an upper part of the FIG. 1 control valve.

Referring first to FIG. 1, the control valve introduces part of refrigerant discharged from a variable displacement compressor, not shown, and allows the introduced refrigerant to flow into a crankcase while controlling the flow rate thereof. The control valve is formed by integrally assembling a valve-forming section 1 containing a valve section for adjusting the flow rate of refrigerant, and a solenoid 2 for controlling the valve lift of the valve section.

The valve-forming section 1 has a stepped hollow cylindrical upper body 3 having an open upper end defining therein a discharge pressure port 4 which communicates with a discharge chamber of the compressor, for receiving discharge pressure Pd, and a strainer 5 capped on the upper body 3 in a manner covering the open upper end of the upper body 3. The discharge pressure port 4 communicates with a crank pressure port 6 opening in a side of a central portion of the upper body 3. The crank pressure port 6 communicates with the crankcase of the compressor, for delivering controlled pressure (crank pressure) Pc to the crankcase. Furthermore, a suction pressure port 7 opens in a side of a lower portion of the upper body 3, for communication with a suction chamber of the compressor for introducing suction pressure Ps, and a refrigerant passage connected to the suction pressure port 7 changes its direction downward inside the upper body 3 to open in a lower end face of the upper body 3.

Formed between the discharge pressure port 4 and the crank pressure port 6 in the upper portion of the upper body 3 is a crankcase-communicating chamber 8 that is filled with the crank pressure Pc. In the center of the lower portion of the upper body 3 is formed a guide hole 9 which axially extends therethrough for having a shaft, referred to hereinafter, inserted therein to guide the same. The guide hole 9 communicates with the crankcase-communicating chamber 8 via an opening at an upper end thereof.

In the top of the upper body 3, a valve seat-forming member 10 having a stepped hollow cylindrical shape is disposed in a manner inserted into the crankcase-communicating chamber 8.

As shown in FIG. 2, the valve seat-forming member 10 has the outer periphery of an upper end thereof press-fitted in the open upper end of the upper body 3, and a lower portion of the valve seat-forming member 10 extends downward through the crankcase-communicating chamber 8 with a diameter reduced by a step. This reduced diameter portion has a root portion formed with communication holes 11 for communication between the inside and the outside of the valve seat-forming member 10. Further, the valve seat-forming member 10 has an intermediate portion of an inner part thereof formed with a valve hole 12 such that a space on the discharge chamber side and a space on the crankcase side communicate with each other, and the rim of an opening of the valve hole 12 on the crankcase side forms a valve seat 13.

A valve element 14 is disposed in a lower opening of the valve seat-forming member 10 in a manner movable axially back and forth. The valve element 14 comprises a holder 15 that is slidable along an inner wall of the valve seat-forming member 10, and a ball 16 that is press-fitted in a central portion of the upper end of the holder 15. The holder 15 has the outer periphery of an upper portion thereof reduced in diameter, and a spring 17 is fitted on the reduced-diameter portion. The spring 17 is interposed between the valve seat-forming member 10 and the holder 15, for urging the ball 16 in a direction away from the valve seat 13. Further, the holder 15 has a side formed with communication holes 15a for communication between the inside and the outside of the holder 15. The ball 16 operates in unison with the holder 15 such that it can be seated on the valve seat 13. The discharge pressure Pd introduced from the discharge pressure port 4 is decompressed by passing through a restriction flow passage between the ball 16 and the valve seat 13, whereby the crank pressure Pc is generated.

Referring again to FIG. 1, a shaft 18 is inserted into the guide hole 9 of the upper body 3 in a manner movable axially back and forth. The shaft 18 has one end extending though the holder 15 to abut the ball 16, and the other end extending downward from the upper body 3.

As described above, since the shaft 18 abuts the valve element 14 not via the holder 15 but via the ball 16 which is disposed ahead of the holder 15 through which the shaft 18 extends, the valve element 14 acts based on the principle of a balancing toy. As a result, a lateral motion of the valve element 14 is suppressed, and hence the valve element 14 is capable of axially moving back and forth in a stable state in which lateral load is reduced. Further, since the lateral load on the valve element 14 generated upon axial movement of the valve element 14 is reduced, hysteresis is decreased in the opening and closing characteristics of the control valve and the lateral displacement of the valve element 14 is suppressed. As a result, complete closing of the valve element 14 can be expected.

The upper body 3 has an upper open end of a lower body 19 joined to a bottom portion thereof by caulking, and a core 20 of the solenoid 2 is screwed onto a lower end of the upper body 3. The core 20 has a central hole 21 axially formed therethrough, and an upper portion of the core 20 is formed with communication holes 22 extending from the outer periphery to communicate with the central hole 21, and communication holes 23 that open in an upper end of the core 20, with one ends of the communication holes 23 communicating with a refrigerant passage connected to the suction pressure port 7 and the other ends of the same communicating with the communication hole 22. With this configuration, the suction pressure Ps is received by an end of the shaft 18.

A sleeve 24 is disposed inside the lower body 19. A stopper 25 in the form of a lid is fitted in a lower opening of the sleeve 24, as viewed in FIG. 1, and an annular bearing member 26 is press-fitted in the inner periphery of the stopper 25. Further, the core 20 screwed onto the upper body 3 and a plunger 27 are arranged in the sleeve 24. The plunger 27 is rigidly fixed to a shaft 28 that has one end extending through the core 20 into an opening in the lower end of the upper body 3 to be supported thereat, and the other end supported by the bearing member 26. Movement of the plunger 27 toward the shaft 18 is restricted by a stop ring 29 fitted on the shaft 28. This enables the plunger 27 to axially move back and forth without being brought into contact with the sleeve 24. Further, a spring 30 is interposed between the core 20 and the plunger 27, and a spring 31 between the plunger 27 and the bearing member 26.

Arranged along the outer periphery of the sleeve 24 are a yoke 32, a solenoid coil 33, and a casing 34 surrounding the yoke 32 and the solenoid coil 33, which constitute the solenoid 2 together with the core 20 and the plunger 27. A handle 36 having a harness 35 inserted therethrough is fitted in the bottom of the casing 34 to close the lower end of the solenoid 2.

Next, the operation of the control valve for a variable displacement compressor will be described in association with the operation of the variable displacement compressor.

In the control valve, the discharge pressure Pd of refrigerant introduced from the discharge chamber acts on the ball 16 from above, as viewed in FIG. 1. On the other hand, the suction pressure Ps introduced from the suction chamber into the central opening 21 via the suction pressure port 7 and the communication holes 23 and 22 acts on the shaft 18 in abutment with the ball 16, from below, as viewed in FIG. 1, via a clearance between the upper body 3 and the shaft 28. As a result, if the diameter of the shaft 18 (i.e. the diameter of the guide hole 9) and the diameter of the valve hole 12 are equal to each other, the effective pressure-receiving area of the ball 16 for receiving the discharge pressure Pd and the effective pressure-receiving area of the shaft 18 for receiving the suction pressure Ps become equal to each other. Therefore, the crank pressure Pc applied to an intermediate formed by making the valve element 14 and the shaft 18 integral with each other is cancelled, and the ball 16 for control of the flow rate of refrigerant flowing from the discharge chamber into the crankcase forms a differential pressure valve that operates by sensing the differential pressure between the discharge pressure Pd and the suction pressure Ps. In the present embodiment, however, the difference between the above-mentioned effective pressure-receiving areas is adjusted e.g. by increasing only one of them, whereby characteristics (differential pressure·crank pressure characteristics) concerning the degree of influence of the crank pressure on a change in the differential pressure between the discharge pressure and the suction pressure are adjusted such that they become desired characteristics. This adjustment will be described in detail hereinafter.

In the control valve for a variable displacement compressor, when control current is not supplied to the solenoid coil 33 of the solenoid 2, the discharge pressure Pd pushes open the ball 16 to place the ball 16 in a fully-open state. As a result, in the compressor, the crank pressure Pc becomes closer to the discharge pressure Pd, whereby the difference between respective pressures applied to opposite ends of each of the pistons disposed in a manner facing the crankcase, for suction and compression of refrigerant becomes the minimum. This causes a swash plate in the crankcase for determining the stroke of the pistons to have an inclination angle which minimizes the stroke, thereby causing the compressor to operate with the minimum capacity or displacement.

Further, when maximum control current is supplied to the solenoid coil 33 of the solenoid 2, the plunger 27 is attracted by the core 20 to be moved upward, as viewed in FIG. 1, whereby the shafts 28 and 18 are pushed upward, as viewed in FIG. 1, to place the ball 16 in a fully-closed state. At this time, from the crankcase, which communicates with the suction chamber via a fixed orifice, not shown, refrigerant is allowed to flow into the suction chamber via the fixed orifice, whereby the crank pressure Pc is reduced to a value close to the suction pressure Ps in the suction chamber. This maximizes the difference between the pressures applied to the opposite ends of each piston, thereby causing the swash plate to have an inclination angle which maximizes the stroke of the pistons, whereby the compressor shifts to an maximum capacity operation.

Now, when normal control is performed to supply a predetermined control current to the solenoid coil 33 of the solenoid 2, the plunger 27 is attracted by the core 20 according to the magnitude of the control current, which generates a force for moving the plunger 27 upward, as viewed in FIG. 1, by a predetermined amount. This force serves as a set value of the control valve that operates as the differential pressure valve. Therefore, the control valve senses the differential pressure between the discharge pressure Pd and the suction pressure Ps, and controls the flow rate of refrigerant flowing from the discharge chamber into the crankcase such that the differential pressure is held at a value corresponding to the set value set by the solenoid 2.

Next, a description will be given of a method of adjusting the differential pressure·crank pressure characteristics of the above-described control valve for a variable displacement compressor.

In the present embodiment, the control valve is configured such that desired differential pressure·crank pressure characteristics can be obtained by adjusting the difference between the effective pressure-receiving area A on the discharge pressure side of the intermediate formed by making the valve element 14 and the shaft 18 integral with each other, and the effective pressure-receiving area B on the suction pressure side of the intermediate, as shown in FIG. 2. It should be noted that the effective pressure-receiving area A on the discharge pressure side can be adjusted by adjusting the diameter of the valve hole 12, and the effective pressure-receiving area B on the suction pressure side can be adjusted by adjusting the diameter of the shaft 18 (i.e. the diameter of the guide hole 9). FIGS. 3A to 3C are diagrams useful in explaining the differential pressure·crank pressure characteristics of the control valve, wherein FIG. 3A represents the case where the effective pressure-receiving area A and the effective pressure-receiving area B are equal to each other, FIG. 3B the case where the effective pressure-receiving area A is smaller than the effective pressure-receiving area B, and FIG. 3C the case where the effective pressure-receiving area A is larger than the effective pressure-receiving area B.

Referring to FIG. 3A, when the effective pressure-receiving area A on the discharge pressure side and the effective pressure-receiving area B on the suction pressure side are equal to each other, the differential pressure (Pd−Ps) between the discharge pressure Pd and the suction pressure Ps is slightly changed under the influence of the crank pressure Pc even when the value of electric current supplied to the solenoid is fixed. The differential pressure (Pd−Ps) varies with the magnitude of the value (Isol) of electric current supplied to the solenoid 2.

More specifically, the effective pressure-receiving area A on the discharge pressure side and the effective pressure-receiving area B on the suction pressure side are equal to each other, so that originally, the crank pressure Pc should be cancelled and the differential pressure (Pd−Ps) should assume a predetermined value, irrespective of the crank pressure Pc, but actually, it is difficult to completely eliminate the influence of the crank pressure Pc, and there appears a slight slope in the characteristics, as shown in FIG. 3A.

Referring to FIG. 3B, when the effective pressure-receiving area A is set to be smaller than the effective pressure-receiving area B, the balance of actions of the crank pressure Pc on the intermediate formed by making the valve element 14 and the shaft 18 integral with each other is lost, and the degree of contribution of the crank pressure Pc in the valve-opening direction becomes larger. This makes the valve section easier to open. As a result, the differential pressure (Pd−Ps) rises promptly, and the influence of the crank pressure Pc becomes smaller than when the effective pressure-receiving area A and the effective pressure-receiving area B are equal to each other, which enhances the response of the swash plate of the compressor.

Referring to FIG. 3C, when the effective pressure-receiving area A is set to be larger than the effective pressure-receiving area B, the balance of actions of the crank pressure Pc on the intermediate formed by making the valve element 14 and the shaft 18 integral with each other is lost, and the degree of contribution of the crank pressure Pc in the valve-closing direction becomes larger. This makes the valve section more difficult to open. As a result, the differential pressure (Pd−Ps) is slow in rising, and the influence of the crank pressure Pc becomes larger than when the effective pressure-receiving area A and the effective pressure-receiving area B are equal to each other, which lowers the response of the swash plate of the compressor.

As described above, by adjusting the difference between the effective pressure-receiving area A and the effective pressure-receiving area B, it is possible to change the differential pressure·crank pressure characteristics of the control valve. Therefore, e.g. when the response of the swash plate of the compressor is desired to be particularly enhanced compared with the characteristics of the conventional control valve, the control valve is only required to be configured such that the effective pressure-receiving area A becomes smaller than the effective pressure-receiving area B. Inversely, when the response of the swash plate is desired to be lowered compared with the characteristics of the conventional control valve, the control valve is only required to be configured such that the effective pressure-receiving area A becomes larger than the effective pressure-receiving area B.

As described heretofore, in the control valve according to the present invention, the difference between the effective pressure-receiving area A on the discharge pressure side of the intermediate formed by making the -valve element 14 and the shaft 18 integral with each other and the effective pressure-receiving area B on the suction pressure side of the intermediate is adjusted as required. This makes it possible to obtain desired differential pressure·crank pressure characteristics according to the specifications of the control valve. Changes in the effective pressure-receiving areas have almost no influence on the electric current·differential pressure characteristics, i.e. the relationship between the value of electric current supplied to the solenoid 2 and the differential pressure between the discharge pressure Pd and the suction pressure Ps, and hence it is possible to realize the changes in the effective pressure-receiving areas with ease.

According to the control valve of the present invention, desired differential pressure·crank pressure characteristics (characteristics concerning the degree of influence of the crank pressure on a change in the differential pressure between the discharge pressure and the suction pressure) can be obtained by adjusting the difference between the effective pressure-receiving area on the discharge pressure side of the intermediate formed by making the valve element and the shaft integral with each other, and the effective pressure-receiving area on the suction pressure side of the intermediate. Since the changes in the effective pressure-receiving areas have almost no influence on the electric current·differential pressure characteristics, i.e. the relationship between the value of electric current supplied to the solenoid and the differential pressure between the discharge pressure and the suction pressure, it is possible to obtain desired differential pressure·crank pressure characteristics with ease.

The foregoing is considered as illustrative only of the principles of the present invention. Further, since numerous modifications and changes will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and applications shown and described, and accordingly, all suitable modifications and equivalents may be regarded as falling within the scope of the invention in the appended claims and their equivalents. 

1. A control valve for a variable displacement compressor, the control valve being mounted in the variable displacement compressor, for controlling pressure in a crankcase of the compressor to thereby vary a discharge capacity of refrigerant, comprising: a body that has a discharge pressure port for introducing discharge pressure of the compressor, a crank pressure port for delivering crank pressure generated in the control valve to the crankcase, and a suction pressure port for introducing suction pressure, the discharge pressure port, the crank pressure port, and the suction pressure port being sequentially arranged from one end of the body; a valve element that is moved to and away from a valve seat provided between the discharge pressure port and the crank pressure port, for reducing the discharge pressure introduced from the discharge pressure port by a restriction passage formed between the valve element and the valve seat to generate the crank pressure; a shaft that supports the valve element in a valve-opening or valve-closing direction and is capable of operating in unison with the valve element; and a solenoid that is connected to an end of the body opposite to the discharge pressure port, and comprises a core, a plunger capable of being made integral with the valve element via the shaft, and a solenoid coil for being energized to generate a magnetic circuit including the plunger and the core, wherein a degree of influence of the crank pressure on a change in differential pressure between the discharge pressure and the suction pressure is adjusted by adjusting a difference between an effective pressure-receiving area of an intermediate for receiving the discharge pressure, the intermediate being formed by making the valve element and the shaft integral with each other, and an effective pressure-receiving area of the intermediate for receiving the suction pressure.
 2. The control valve according to claim 1, wherein a crankcase-communicating chamber filled with the generated crank pressure and having the valve element disposed therein is defined between the valve seat and the crank pressure port of the body, wherein a guide hole is formed in the body on a side opposite to the discharge pressure port in a manner coaxial with a valve hole defining the valve seat, the guide hole opening into the crankcase-communicating chamber and having the shaft inserted therein for guiding the shaft, wherein the shaft is configured to receive the suction pressure on a side of the guide hole opposite to the crankcase-communicating chamber, wherein the effective pressure-receiving area of the intermediate for receiving the discharge pressure is adjusted by a size of a cross-sectional area of the valve hole, and wherein the effective pressure-receiving area of the intermediate for receiving the suction pressure is adjusted by a size of a cross-sectional area of the guide hole.
 3. The control valve according to claim 2, wherein the effective pressure-receiving area of the intermediate for receiving the discharge pressure is configured to be larger than the effective pressure-receiving area of the intermediate for receiving the suction pressure, whereby the degree of the influence of the crank pressure on the change in the differential pressure between the discharge pressure and the suction pressure is made larger than when the two effective pressure-receiving areas are equal to each other.
 4. The control valve according to claim 2, wherein the effective pressure-receiving area of the intermediate for receiving the discharge pressure is configured to be smaller than the effective pressure-receiving area of the intermediate for receiving the suction pressure, whereby the degree of the influence of the crank pressure on the change in the differential pressure between the discharge pressure and the suction pressure is made smaller than when the two effective pressure-receiving areas are equal to each other. 